The present invention relates to a piezo-electric knock sensor for sensing knocking of internal combustion engines.
According to the conventional piezo-electric knock sensor, vibration caused by the knocking of the internal combustion engine is detected by transmitting the vibration of a weight to a piezo-electric element via a spring which resonates at a knocking frequency of the internal combustion engine and which is separately provided from the weight. The above knock sensor has been disclosed, for example, in FIG. 1 of Japanese Patent Laid-Open No. 19978/1980.
In the conventional piezo-electric knock sensor, however, since vibration of weight provided separately from the spring is transmitted to the piezo-electric element via the spring as mentioned above, it is difficult to compactly design the device which resonates only at such high frequencies of about 7 to 8 KHz that are equal to knocking frequencies of the internal combustion engines.